1. Field of the Invention
This invention relates to a valve and, more particularly, a valve for controlling the flow of cryogenic fluid.
2. Discussion of the Related Art
Cryogenic fluids, such as liquid nitrogen, liquid oxygen or the like, are often stored on-site at a facility for use in various applications. For example, a hospital may store liquid oxygen on-site for medical uses, or a company may store liquid nitrogen at its facility for manufacturing processes. Conventionally, a cryogenic fluid is held in a storage tank at a temperature and pressure that maintains the fluid in a liquid state for future usage in a gaseous state.
Cryogenic fluids are conventionally delivered to a facility in a transportable supply tank from which the fluid can be pumped through a fluid delivery system into the storage tank. The fluid delivery system often includes a complex arrangement of valves and piping for controlling the flow of fluid to the storage tank, as well as for preventing fluid leakage from the tank. The cryogenic fluid typically is pumped to both the top and the bottom of the storage tank requiring that the piping be split into two feed lines which are connected to the top and bottom of the storage tank.
Under some circumstances, cryogenic fluid may inadvertently flow out of the storage tank and either back through the fluid delivery system into the supply tank or escape into the atmosphere. For example, when transferring fluid to the storage tank, the pressure in the storage tank may exceed the capacity of the fluid delivery pump resulting in reverse flow from the storage tank into the supply tank. As another example, an individual may fail to close one or more valves resulting in fluid leakage onto the ground or into the atmosphere from the storage tank when the supply tank is disconnected from the storage tank.
Valves have been proposed that utilize a poppet check valve to prevent inadvertent reverse flow through the valve housing. Poppet check valves, however, are typically complex mechanisms that utilize preloaded springs for actuating the poppet valve in response to a predetermined pressure differential across the check valve.
Valves for use at cryogenic temperatures face an increased possibility of leakage through relatively small openings or seams due to shrinkage of the valve components when subjected to cryogenic temperatures. Thus, cryogenic valves require precisely fabricated valve components to ensure fluid tight shell and seat performance. The introduction of foreign matter or debris into the valve can interfere with the valve components, particularly the valve seat seals, resulting in fluid seepage through the valve. Additionally, unfiltered debris, particularly large scale debris, that pass through the fluid delivery system can potentially interfere with the operation of process equipment or other systems within the facility.
In view of the foregoing, it is an object of the present invention to provide an improved valve, particularly a valve for use with cryogenic fluids, that reduces the possibility of inadvertent reverse flow through the valve and limits the introduction of foreign matter.